(1) Field of the Invention
This invention relates to a syringe device and, more particularly, to a non-reusable retractable syringe having an automatically retracting hypodermic needle to prevent reuse of the syringe. A method for delivering fluid to a patient and retracting the needle within the syringe after the fluid is delivered is disclosed.
(2) Description of Problems and the Prior Art
Many communicable diseases are commonly spread by contacting bodily and/or medicinal fluids of an infected person, reuse of hypodermic syringes is one of the most common causes of such contact.
Various mechanisms are provided in medical facilities for the disposal or destruction of syringes and hypodermic needles after usage. However, it is not uncommon for a medical worker to be scratched or punctured by a needle after usage and before disposal, resulting in injury and exposure to disease. Accordingly, there exists a need to protect personnel from accidental skin injuries from such contaminated needles, as well as the need to provide a safe and efficient means for disposing of the needles themselves.
There has been increased emphasis in designing hypodermic syringes with extendible shields which protect and project over the needle area after injections are completed. Such devices often involve manual manipulation of the shield over the needle after the injection is completed. It follows that when the shield is manually extended over the needle, the operator's hands or fingers may come into contact with the tip of the needle, thus causing risk of infection. To correct this problem, many devices have built-in biasing means which provide a shield over the needle after the injection is completed.
In U.S. Pat. No. 5,053,010, entitled "Safety Syringe with Retractable Needle", issued Oct. 1, 1991, there is shown and disclosed an improved safety syringe with retractable needle which allows retraction of the needle into a hollow plunger by additional forward pressure on the plunger after fluid is driven from the syringe into the patient. The syringe includes a hollow plunger which is inserted into one end of a cylindrical barrel and a hollow needle attached to the other end of the barrel. Biasing means are attached to the barrel for biasing the needle towards the hollow plunger, and means are provided for releasing the needle into the hollow plunger by applying additional forward pressure upon the plunger after the plunger is telescopically contracted relative to the barrel. This design, as well as others which are commercially available, provide a plunger which is made of a plastic material, such as polypropylene, which is manufactured by known techniques. Typically carried thereon is a sealing element which is made of a comparatively soft elastomeric material, which forms the seal between the housing and the moving plunger, to prevent leakage therebetween of the fluid to be injected.
The design disclosed in U.S. Pat. No. 5,053,010 incorporates a sliding elastomeric seal which displaces from its forward position to a retracted position, thereby allowing additional forward travel of the plunger to actuate the retraction mechanism. However, with this configuration, the soft nature of the seal depicted could allow it to slide prematurely during an injection. Increasing the stiffness of the sealing member would reduce the tendency to slide prematurely, but at the expense of the seal integrity.
There is need for an improved design of syringe in which an elastomer or other relatively soft seal can be used to provide maximum sealing integrity while also permitting sufficient pressure to be applied through the device to complete the injection, and thereafter to permit a cutter operatively associated with the plunger to continue to travel to cut the seal and, in turn, initiate retraction of the needle into the device after completion of the injection.
Moreover, it has been found desirable to prevent telescopic expansion of the plunger relative to the barrel of the device after activation of the retraction mechanism to assure that the needle tip cannot easily be re-exposed through withdrawal of the plunger.